1. Field of the Invention
The present invention relates to a silver halide photographic material, and more particularly, to a silver halide photographic material having improved image quality.
2. Description of the Prior Art
Silver halide photographic materials (hereunder simply referred to as photographic materials) generally consist of a support such as glass, paper or synthetic resin film having formed thereon photosensitive silver halide emulsion layers, as well as nonsensitive hydrophilic colloidal layers such as a filter layer, an intermediate layer, a protective layer, a subbing layer, a backing layer and an antihalation layer. The thicknesses of the photographic materials vary with the type of the specific photographic material and what constituent layers are used. Color photographic materials using more than 10 constituent layers may exceed 20 microns in thickness.
With the recent development of smaller formats for pictures and with the increasing demand of users for higher image quality, the need for photographic materials having improved image quality is increasing. One proposal for improving the image quality is by decreasing the thickness of each of the layers coated on the photographic support. This technique is considered to be effective for increasing the image sharpness because it reduces not only the optical scattering path but also the diffusion path occurring in the development process. However, this method has its own problem.
The layers formed on the photographic support generally consist of a hydrophilic colloid (binder) having dispersed therein silver halide grains and various additives that suit specific purposes. The additives include water-insoluble compounds such as high-boiling organic solvents, and they are incorporated in the binder in the form of emulsified oil globules. Photographic additives may also be incorporated within these oil globules to achieve various purposes. For example, UV absorbers may be incorporated for the purposes of preventing static buildup or improving the keeping quality. Anti-discoloration agents or anti-oxidants may be incorporated in order to provide improved keeping quality. Other additives that can be incorporated in oil globules are oil-soluble couplers; DIR compounds that react with the oxidation product of a developing agent to release a development retarding compound and form a substantially colorless compound; agents to prevent color mixing; and anti-stain agents.
If the oil globules are present in each constituent layer at a higher density than the binder, they coalesce in a hot and humid atmosphere and cause "bleeding" that either makes the surface of the layer sticky or may even devitrify the surface of the photographic material.
A method is shown in Japanese Patent Publication No. 8346/81 for minimizing the "bleeding" by reducing the density of the oil globules in the outermost photographic layer. However, in order to provide an improved image sharpness, the thickness of each photographic layer must be reduced by using less gelatin, and this increases unavoidably the density of the oil globules. Therefore, this method is not completely effective for preventing the "bleeding".